1. Field of the Invention
The present invention relates to positioning systems, and more particularly to a cantilevered system for positioning a work piece along the X-Y axis of a semi-automatic fastener insertion machine or press for the insertion of self-clinching fasteners into the work piece.
2. Description of the Prior Art
Mass production of duplicate parts is well known in the metal parts manufacturing industry. A wide variety of flat sheet metal parts have been developed in the past and will be developed in the future. Often, the design of a given sheet metal part requires that it include one or more self-clinching fasteners or nuts. For example, in the automotive industry, many components of various kinds are attached to sheet metal parts (plates or panels). In order for these attachments to take place, self-clinching fasteners or nuts must be built or inserted into the sheet metal of the part. The threaded hole in the fastener or nut is then used to receive a screw or bolt from a different component part allowing the component part to be attached to the sheet metal part.
Numerous insertion machines and presses have been developed over the years which insert fasteners into sheet metal parts. In mass production situations, it is important that such insertions be consistent on every part for interchangeability and reliability. It is therefore desirable to provide a support system for the metal sheet (the work piece) that allows consistent and reliable positioning of the work piece in the insertion machine.
Often, the shape of a work piece is such that it must be moved or removed and replaced in the press in order for all of the fasteners to be inserted thereon. The need to move and reposition a work piece is particularly apparent when the work piece is not flat, but instead has two or more surfaces on different planes joined at an angle. Only one planar surface of such work pieces may be operated upon at a time, requiring the work piece to then be removed and repositioned such that a different surface of the same piece is placed in the operating position. Existing positioning systems have been designed to work on only a single planar surface, and none is capable of performing such repositioning.
A number of electronically controlled positioning systems exist which may be programmed to raise and lower the work piece along the Z-axis, and to move it from one position to another on the X and Y axes. Simple work piece holders such as those described in U.S. Pat. Nos. 3,777,602 and 3,848,495 describe a die fixture and control apparatus for positioning a work piece below a punch press. More complex work piece holders and clamps are described in U.S. Pat. Nos. 4,565,358; 4,775,135; 5,222,719 and 5,487,539. However, none of these patents teach an apparatus that allows for easy removal and repositioning of different surfaces of the same work piece; in particular, none of them teach the use of cantilevered support.
A related problem arises when the metallic work piece sheets themselves are not formed in a completely consistent manner. In mass production situations, the thickness of the metallic sheets and the positions of the pre-cut holes into which the fasteners are to be inserted may vary by several thousandths to several hundredths of an inch, depending upon the metal and the part. Such variations are generally not tolerable by insertion machines with ordinary positioning systems. This can result in mis-positioned or mis-located fasteners, angled or bent fasteners, or failure of the fastener to be inserted at all.
The flexibility of the devices disclosed in the above identified patents are also limited as a result of the use of trays and clamp means to hold the work piece firmly in place. Such trays and clamps prevent any contemporaneous adjustment of the work piece in response to variations or inconsistencies in form.
The use of alignment pins to support a work piece is taught in U.S. Pat. Nos. 3,417,458 and 5,566,840. The function of the alignment pins in each of these patents is to hold the work piece in a precise location despite possible variations in the work piece itself. Such pins are smaller than the openings on the work piece into which they fit, but the pins are positioned so that they create opposing forces in the work piece resulting in fixed positioning of the work piece itself.
In addition to the above, the following U.S. Patents are also known to exist:
______________________________________ U.S. Pat. No. Date Inventor ______________________________________ 2,147,800 February 21, 1939 Sadowski 2,547,211 April 3, 1951 Holmes 3,216,717 November 9, 1965 Bagge, et al 3,240,485 March 15, 1966 Oser 4,140,306 February 20, 1979 Wheeler 4,545,570 October 8, 1985 KaDell, Jr. 4,637,303 January 20, 1987 Lucky 5,538,231 July 23, 1996 Baldwin 5,573,230 November 12, 1996 Lambertini ______________________________________